Linked List in JS

ll.js

function Node(data, { left, right } = {}) {
  this.data = data
  this._left = left || this,
  this._right = right || this
}

Node.prototype = {
  left,
  right,
  insertLeft,
  insertRight,
  remove,
  toArray
}

function left() {
  return this._left
}

function right() {
  return this._right
}

function insertLeft(data) {
  const left = new Node(data, { left: this.left(), right: this })
  this._left._right = left
  return this._left = left
}

function insertRight(data) {
  const right = new Node(data, { left: this, right: this.right() })
  this._right._left = right
  return this._right = right
}

function remove() {
  this._left._right = this._right
  this._right._left = this._left
  return this
}

function toArray(direction = 'right') {
  const array = [this.data]
  let node = this
  while (this !== (node = node[direction]())) {
    array.push(node.data)
  }

  return array
}